Performance evaluation of DC motors for electric rope shovels based on air gap flux measurement

DC motors remain an attractive solution for mining applications, such as rope shovels and draglines, due to their robustness, good dynamic performance and vast experience accumulated within the industry. To achieve optimal performance of the DC machines under increasingly demanding operation conditions, it is important to thoroughly understand their performance limitations under conditions dictated by mining environment. For this purpose, a unique test facility has been developed in Hunter Valley (NSW, Australia) to be able to complete extensive experiments, under controlled conditions, on the full size DC motors used by Australian mining industry. This paper will explain about the structure of the facility, the test methodology and the instrumentation. The main focus of the experimental program is to obtain real time measurements of flux distribution in the air gaps of the DC machines, together with other important parameters. Physically measured flux distribution under different conditions will allow to accurately determine a variety of important characteristics, including electromagnetic conditions of commutation. To the best of the authors' knowledge, only theoretical or indirectly obtained results on flux distribution in the air gap are currently available. The paper includes theoretical predictions as well as experimentally measured flux distributions for two commonly used types of DC motors, physical interpretation of these results and their relation to the motors' performance.